The fixed brackets of an aircraft structure are used to position and support systems in said structure. These systems are paths for electrical cables or piping that transports various fluids, cabin fitting elements such as brackets for luggage racks or equipment.
These brackets are generally fastened to the structure of the fuselage by rivets or structural bonding. In the case of a commercial aircraft, such as a wide-body airplane, the number, kind and positioning of these brackets vary from one plane to another, depending on the fittings options chosen by the airline operating said aircraft. Accordingly, said brackets must be positioned and fastened on the structure upon request. The required positioning accuracy is of the order of one millimeter.
It is known from the prior art to use a laser projector to project the outline of said brackets onto the structure at their planned positions and in this way to facilitate the work of the team in charge of fastening said brackets to the aircraft's structure. These devices are, however, complicated to use and do not, in general, make it possible to achieve the required level of accuracy. The main difficulty is in obtaining a known and stable positioning of the projector within the aircraft structure. In effect, such a projector uses the information from a digital model, which comprises the geometric definition of the brackets as well as their position and orientation within the structure, to calculate the corrections required to the projection so that the projected outline is identical to the outline of the object to be positioned. These correction factors take into account, in particular, the exact distance from the focal point of the projection lens to the projection surface, and the angle between the optical axis and the normal to said surface. For this reason, these parameters must be perfectly known and able to be determined.
In addition, because the aircraft's structure at this stage of the assembly is bristling with structure elements such as frames, stringers or mountings, there are optimum positions of the projector that provide access to a maximum volume of visibility, i.e. these remarkable positions of the projector allow a maximum number of outlines to be projected on the structure without the beam being obscured by the elements making up said structure.
According to the prior art, the projector is placed on a tripod, often outside the structure, whose position in relation to this structure cannot be known accurately. In addition, this position is not stable. Consequently, the required accuracy cannot be achieved.